DESCRIPTION (Applicant's Abstract): Psychiatric comorbidity, particularly depression, occurs often in substance abusers, and is associated with poor outcome. However, previous diagnostic instruments have been unreliable, controversy has surrounded the concepts of comorbidity diagnosis, and results of treatment studies have been inconsistent. In particular, questions persist on whether a treatment-responsive depressive disorder exists in non-abstinent substance abusers. For treatment research to begin to accumulate meaningful results on substance abuse comorbidity, concepts and diagnoses must be clear and reliable. To begin to address this problem, we developed the DSM-111-R Psychiatric Research Interview for Substance and Mental Disorders (PRISM), which showed very good test-retest reliability for primary major depression and other DSM-111-R mental disorders in substance abuse and psychiatric patients. To address the problem of current DSM-IV diagnosis of depression and other disorders in non-abstinent substance abusers, we developed a new version of the PRISM. This version uses phenomenologically-oriented methods for differentiating between primary disorders, substance-induced disorders, and the expected effects of intoxication/withdrawal. These PRISM methods were carefully designed to be consistent with DSM-IV. A reliability and validity test of the new PRISM is needed, with special focus on the differentiation between current primary depression, substance-induced depression and expected intoxication/withdrawal effects. We propose such a study in 510 methadone maintenance and dual diagnosis psychiatric patients. Interviews will be conducted by clinicians. The sample will allow for separate reliability coefficients for each site. Subjects will be sampled to ensure stable reliability estimates for African-American as well as white patients. The data will also allow tests of the effects of demographic, clinical and process factors on reliability. An initial validity study will also be conducted, focused on the PRISM differentiation between primary major depression, substance-induced major depression, and the expected effects of intoxication/withdrawal. For the validity study, we will use family history and in-person expert psychiatrist evaluation of the need for antidepressant treatment as validators. If the PRISM shows good reliability and validity, it will offer a significant methodological advance for treatment research in substance abusers with psychiatric comorbidity. The study results will provide empirical evidence that is likely to be useful in formulating DSM-V.